I’m looking for a compact antenna solution for the RFM22 434 MHz transceiver. I’m completely unfamilar with RF so this solution needs to be fool proof as well. I have found two antennas that look interesting:
I read that (ceramic?) chip antennas are very sensitive to ground plane size, is that the case with these two? Or can I make an approximation and be fine?
In the Rainsun layout guide the module is located in the middle of the ground plane, that’s not a problem? Can I do the same with the Splash, since the recommended ground plane there is rather large?
Do I need a double sided board? This seems to be the case looking at the Splatch datasheet, but in the Rainsun layout guide (bottom page 2) there is a design where the microstrip (that’s what it’s called right?) runs through the ground plane.
Concerning the Rainsun designs: why does the antenna need to “touch ground” in one design and not the others?
Rainsun: do I need to implement the matching network? Where on the board should it be located?
I am not sure this is too late for you or not but patch antennae as well as ceramic antennae should not have any ground plane under them. The PC layout should follow well respected ground layouts and at least in the region near the antenna the ground should be as complete as possible. Minimize runners through the ground for at least a quarter wave length from the antenna. For 433 MHz that will be about 17 cm.
Patch antenna are not as affected by human body effect as much as other types of antennae, ie PCB loops and other configuration. Essentially patch antennae are a form of a slot antenna and are more an H field antenna than an E field antenna. I am personally working on a shield for the Arduino that will incorporate the RFM22 and some connectors to control a pair of stepper motors for a telescope. I am using the Lynx 433 Splatch Antenna.
If you have any experience with that antenna then please report back here with results.
No it’s not too late, thanks for your reply. I will post here when I manage to build something that works, and I’d be happy to learn about your telescope mount, good luck with that!
please clarify how placing a ground plane under the antenna should be avoided, yet “at least in the region near the antenna the ground should be as complete as possible”.
It depends on the antenna style, but often PCB mounted antennas will require the antenna to be very specifically placed with respect to the ground plane. Often this will mean that the ground plane will have to stop a set distance away from the antenna. This is because the antenna will often use the ground-plane as a virtual part of the antenna. (for example, this picture has no ground plane underneath the antenna, http://colinkarpfinger.com/blog/wp-cont … 1-03-L.jpg , but the ground plane is complete up to the antenna, extending to both sides of the PCB). Every chip antenna will have it’s own specific requirements that it is designed for, and violating those ground requirements will reduce, or outright ruin, the antenna’s performance. These requirements will be documented in the antenna’s datasheet.
PCB mounted antennas common at 2.4GHz but at 433MHz or 900MHz there’s just no substitute for a wire or coaxial rubber-ducky. The PCB mounts at the sub-GHz frequency have negative gain. The most basic antenna is a 1/4 wavelength long dipole. At the lower frequencies, this becomes several inches.
Even 6 in. of wire, though not a 1/4 wavelength, will be markedly better than a PCB antenna. There are helical coil antennas for sub-GHz, but these too have negative gain.
So if the range requirements are very modest, a sub-GHz antenna with PCB traces can suffice.
